首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   9275篇
  免费   107篇
  国内免费   18篇
教育   6271篇
科学研究   1040篇
各国文化   90篇
体育   992篇
综合类   6篇
文化理论   96篇
信息传播   905篇
  2021年   69篇
  2020年   122篇
  2019年   175篇
  2018年   237篇
  2017年   252篇
  2016年   218篇
  2015年   153篇
  2014年   216篇
  2013年   1689篇
  2012年   199篇
  2011年   196篇
  2010年   169篇
  2009年   152篇
  2008年   169篇
  2007年   193篇
  2006年   160篇
  2005年   150篇
  2004年   141篇
  2003年   168篇
  2002年   138篇
  2001年   157篇
  2000年   157篇
  1999年   155篇
  1998年   72篇
  1997年   74篇
  1996年   109篇
  1995年   77篇
  1994年   95篇
  1993年   87篇
  1992年   153篇
  1991年   146篇
  1990年   137篇
  1989年   136篇
  1988年   114篇
  1987年   116篇
  1986年   138篇
  1985年   134篇
  1984年   107篇
  1983年   129篇
  1982年   110篇
  1981年   104篇
  1980年   93篇
  1979年   165篇
  1978年   110篇
  1977年   108篇
  1976年   104篇
  1975年   79篇
  1974年   89篇
  1972年   70篇
  1971年   70篇
排序方式: 共有9400条查询结果,搜索用时 31 毫秒
201.
A mathematical analysis of sequential fault transients due to series and shunt faults is important in the study of circuit breaker pole openings and reclosings with arc resistances. The line loading itself becomes unbalanced momentarily due to load switching. Each double fault is developed in sequence, therefore the initial currents in the second and third fault must be treated properly under transient conditions. New sequence component variables λμ0 and ρσ0 are used with αβ0 components. This study is useful for small power systems as well for large power systems. A digital simulation of various series and shunt faults is presented in a generalized manner using αβ0, λμ0 and ρσ0 components.  相似文献   
202.

Introduction

Extremely high glucose concentrations have been shown to interfere with creatinine assays especially with Jaffe method in peritoneal dialysate. Because diabetes is the fastest growing chronic disease in the world, laboratories study with varying glucose concentrations. We investigated whether different levels of glucose spiked in serum interfere with 21 routine chemistry and thyroid assays at glucose concentrations between 17-51 mmol/L.

Materials and methods

Baseline (group I) serum pool with glucose concentration of 5.55 (5.44-5.61) mmol/L was prepared from patient sera. Spiking with 20% dextrose solution, sample groups were obtained with glucose concentrations: 17.09, 34.52, and 50.95 mmol/L (group II, III, IV, respectively). Total of 21 biochemistry analytes and thyroid tests were studied on Abbott c8000 and i2000sr with commercial reagents. Bias from baseline value was checked statistically and clinically.

Results

Creatinine increased significantly by 8.74%, 31.66%, 55.31% at groups II, III, IV, respectively with P values of < 0.001. At the median glucose concentration of 50.95 mmol/L, calcium, albumin, chloride and FT4 biased significantly clinically (-0.85%, 1.63%, 0.65%, 7.4% with P values 0.138, 0.214, 0.004, < 0.001, respectively). Remaining assays were free of interference.

Conclusion

Among the numerous biochemical parameters studied, only a few parameters are affected by dramatically increased glucose concentration. The creatinine measurements obtained in human sera with the Jaffe alkaline method at high glucose concentrations should be interpreted with caution. Other tests that were affected with extremely high glucose concentrations were calcium, albumin, chloride and FT4, hence results should be taken into consideration in patients with poor diabetic control.Key words: assay interference, glucose interference, preanalytical phase, creatinine, Jaffe kinetic assay, thyroid function tests  相似文献   
203.
Prostate Specific Antigen (PSA) has emerged as the most applicable and important tumor marker for carcinoma prostate. In the present study PSA was determined in serum of healthy subjects, patients of benign prostate hypertrophy (BPH) and Carcinoma Prostate (Ca−P) to evaluate its diagnostic efficiency in day to day management of prostate cancer patients and in differentiating patients of early prostate cancer from those with BPH. Receiver operating characteristic curve (ROC) revealed 2 ng/ml and 10 ng/ml cut off serum PSA level for BPH and untreated carcinoma prostate patients (Ca−P). An extremely significant increase (P<0.0001) was observed in mean PSA concentration in BPH patients and adenocarcinoma prostate patients when compared to healthy males. Clinical relevance of PSA was highlighted by a case study of cancer patient prior to any therapy till death.  相似文献   
204.
Externalities as conventionally defined miss many of the spillovers that are both causes and consequences of the technological changes that underlie economic growth. We introduce a much wider concept called technological complementarities. New general purpose technologies (GPTs) rejuvenate the growth process by creating technological complementarities, which are adequately measured neither by total factor productivity (TFP) nor by externalities. There would be major gains from technological change even if the returns on capital invested in innovation never exceeded the returns on investing in existing technologies so that there were neither externalities nor positive changes in TFP.  相似文献   
205.
Previous papers on grey literature by the authors have described (1) the need for formal metadata to allow machine understanding and therefore scalable operations; (2) the enhancement of repositories of grey (and other) e-publications by linking with CRIS (Current Research Information Systems); (3) the use of the research process to collect metadata incrementally reducing the threshold barrier for end-users and improving quality in an ambient GRIDs environment. This paper takes the development one step further and proposes “intelligent” grey objects. The hypothesis is in 2 parts: (1) that the use of passive catalogs of metadata does not scale (a) in a highly distributed environment with millions of nodes and (b) with vastly increased volumes of R&D output grey publications with associated metadata; (2) that a new paradigm is required that (a) integrates grey with white literature and other R&D outputs such as software, data, products and patents (b) in a self-managing, self-optimizing way and that this paradigm manages automatically curation, provenance digital rights, trust, security and privacy. Concerning (1) existing repositories provide catalogs; harvesting takes increasing time ensuring non-currency. The end-user expends much manual effort/intelligence to utilize the results. The elapsed time of (1) the network (2) the centralized (or centrally controlled distributed) catalog server searches (3) end-user intervention becomes unacceptable. Concerning (2) there is no paradigm currently known to the authors that satisfies the requirement. Our proposal is outlined below. Hyperactive combines both hyperlinking and active properties of a (grey) object. Hyperlinking implies multimedia components linked to form the object and also external links to other resources. The term active implies that objects do not lie passively in a repository to be retrieved by end-users. They “get a life” and the object moves through the network knowing where it is going. A hyperactive grey object is wrapped by its (incrementally recorded) formal metadata and an associated (software) agent. It moves through process steps such as initial concept, authoring, reviewing and depositing in a repository. The workflow is based on the rules and information in the corporate data repository with which the agent interacts. Once the object is deposited, the agent associated with it actively pushes the object to the end-users (or systems) whose metadata indicate interest or an obligation in a workflowed process. The agents check the object and user (or system) metadata for rights, privacy, security parameters, and for any charges and assure compatibility. Alternatively the object can be found passively by end-user or system agents. The object can also associate itself with other objects forming relationships utilising metadata or content. Declared relationships include references and citations; workflowed relationships include versions and also links to corporate information and research datasets and software; inferenced relationships are discovered relationships such as between documents by different authors developed from an earlier idea of a third author. Components of this paradigm have been implemented to some extent. The challenge is implementing—respecting part two of the hypothesis—the integration architecture. This surely is harnessing the power of grey.
Anne AssersonEmail:
  相似文献   
206.
After decades of meager results in school improvement efforts that work and that last, it may seem irrational to hope that this time it could be different—that we could learn and apply approaches to lasting school improvement. Obama (2006, The audacity of hope. New York: Crown publications) might refer to such hope as audacious. What gives us the impulse for hope in the face of continued disappointment? This is not to suggest that all of our efforts have come to naught. Having witnessed and participated in hopeful approaches for more than 40 years, I’ve seen noteworthy programs and heard exceptionally wise ideas. Islands of hope existed in each decade, yet even these remarkable islands drop below sea level when founders, principals or key teachers leave. As long as any one individual is indispensable, sustainability is a distant dream. As I’ve talked with educators, parents, students and community members over these years, I’ve been bombarded with questions. The question I find most compelling is: “We can now understand our schools as they exist. And, we have an improving image of what sustainable schools look like, but how do we get there from here? How do we find our way to the sustainability we yearn for?  相似文献   
207.
Goat ovaries were collected from the slaughterhouse and categorized as right, left, corpus luteum (CL)-present and -absent group and evaluated on the basis of weight (g), length (cm), width (cm), number of follicles, follicles aspirated and number and state ofcumulus-oocyte-complexes (COCs). Comparatively higher weight [(0.66±0.02) vs (0.64±0.02) g], length [(1.17±0.02) vs (1.1 ±0.02) cm] and width [(0.77±0.02) vs (0.74±0.02) cm] were found in right ovaries than those of left. On the other hand significantly (P〈0.05) higher weight [(0.71±0.03) vs (0.64±0.01) g] and width [(0.76±0.03) vs (0.75±0.01) cm] were found in CL-present group than those of CL-absent group of ovaries. The left ovaries contained comparatively higher number of normal COCs [(1.06±0.09) per ovary] than fight ovaries [(1.03±0.10) per ovary] and the similar trend was found in total number of follicles [(4.51±0.25) vs (4.30±0.23) per ovary] and follicles aspirated [(2.55±0.14) vs (2.52±0.12) per ovary]. But the total COCs per ovary was almost similar in both ovaries [right and left: (1.85±0.12) and (1.85±0.11) per ovary, respectively]. Higher number of total COCs [(1.87±0.09) vs (1.76±0.16) per ovary], total number of follicles [(4.45±0.19) vs (4.16±0.37) per ovary], follicles aspirated [(2.55±0.10) vs (2.48±0.21) per ovary] and normal COCs [(1.12±0.07) vs (0.76±0.14) per ovary] were found in CL-absent group than those of CL-present group of ovaries.  相似文献   
208.
Marital conflict and conduct problems in Children of Twins   总被引:3,自引:0,他引:3  
The Children-of-Twins design was used to test whether associations between marital conflict frequency and conduct problems can be replicated within the children of discordant twin pairs. A sample of 2,051 children (age 14-39 years) of 1,045 twins was used to estimate the genetic and environmental influences on marital conflict and determine whether genetic or environmental selection processes underlie the observed association between marital conflict and conduct problems. Results indicate that genetic and nonshared environmental factors influence the risk of marital conflict. Furthermore, genetic influences mediated the association between marital conflict frequency and conduct problems. These results highlight the need for quasiexperimental designs in investigations of intergenerational associations.  相似文献   
209.
This study examined to what extent adolescents’ and their friends’ risk behaviors (i.e., delinquency and alcohol use) hinder or promote their academic achievement (grade point average [GPA]), and vice versa. Longitudinal data were used (= 1,219 seventh- to ninth-grade adolescents; Mage = 13.69). Results showed that risk behaviors negatively affected adolescents’ GPA, whereas GPA protected against engaging in risk behaviors. Moreover, adolescents tended to select friends who have similar behaviors and friends’ behaviors became more similar over time (same-behavior selection and influence). Furthermore, although same-behavior effects seemed to dominate, evidence was found for some cross-behavior selection effects and a tendency in seventh grade for cross-behavior influence effects. Concluding, it is important to investigate the interplay between different behaviors with longitudinal social network analysis.  相似文献   
210.
Research‐practice partnerships offer counselor educators an opportunity to generate scholarship that can promote client welfare and create systemic change in practice and policy. The purpose of this article is to articulate strategies for building and sustaining research‐practice partnerships, as well as suggest methods for evaluating these partnerships.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号